1. Field of Invention:
This invention relates isocyanate-containing acrylic polymers and more particularly to low molecular weight polymers having a terminal thioalkyl group and low toxicity.
2. Prior Art:
Acrylic polymers containing pendent isocyanate groups are known.
U.S. Pat. No. 2,718,516, issued Sept. 20, 1955 to N. M. Bortnick, describes high molecular weight polymers, containing a plurality of isocyanate groups, based on (meth) acrylic ester isocyanates. The polymers obtainable by the described method are often intractable when the polymerization is carried to completion or when high levels of the isocyanate monomers are used during the polymerization.
Other types of organic polyisocyanates useful as crosslinking agents are also well known.
U.S. Pat. No. 3,124,605, issued Mar. 10, 1964, to K. Wagner, describes low molecular organic polyisocyanates having the following biuret structure: ##STR3## where R is an aliphatic, hydroaromatic, araliphatic, including aralkyl, or an aromatic radical, which may or may not be substituted; and X is hydrogen or --CO--NX--R--NCO. A commercially available example of such an isocyanate, where R is (CH.sub.2).sub.6 and X is hydrogen, has recently been found to contain, upon aging, excessive levels of a residual monomeric diisocyanate, thereby increasing the toxicity.